The induction of antigenic modulation of leukemic cells, the modalities of enhancing and inhibiting such changes and the relationships between expression of antigenicity and cellular capacity to transplant and metastasize will be further studied. The local cellular reaction to tumor cells of various antigenic expression in transplanted tumors and in their metastases will be examined histologically and immunologically. The conversion in vitro of leukemic cells expressing viral-associated antigens (GLV plus) to cells lacking antigenicity (GLV minus) will be induced by the supplementation of media with anti GLV sera. The redistribution of membrane antigens that occurs under these conditions will be studied in relation to the phases of the cell cycle. The reversion of GLV minus cells to GLV plus cells by explantation in vitro will be analyzed in blocking and enhancing experiments.